The present invention relates to a valve control apparatus for an internal combustion engine, which is able to vary a characteristic such as a lift amount of intake valve and/or exhaust valve in accordance with an operating state of the engine.
Japanese Patent Application Publication No. 2009-103040 discloses a previously-proposed valve control apparatus in the field. This valve control apparatus includes a holder which varies its swing position by a control cam, and a sub-cam which is driven by an intake cam and which swings about a support shaft fixed to the holder. The sub-cam includes a drive cam surface and a rest cam surface. The drive cam surface drives a first intake valve through a first rocker arm. The rest cam surface drives a second intake valve through a second rocker arm. Moreover, the valve control apparatus further includes a connection changeover mechanism which connects the first rocker arm with the second rocker arm or disconnects the first rocker arm from the second rocker arm.
In a high-load region of engine, the connection changeover mechanism connects the first rocker arm with the second rocker arm so that both of the first and second intake valves are driven (opened and closed) by the drive cam surface which produces a large lift. Thereby, an intake-air charging efficiency is enhanced to increase an output torque of the engine.
On the other hand, in a low-load region of the engine, the connection changeover mechanism disconnects the first rocker arm from the second rocker arm. Thereby, the first intake valve is driven by the drive cam surface, and the second intake valve is made substantially in a closed state (minute-lift state) by the rest cam surface which produces a small lift. Because of this lift difference between the first and second intake valves, an intake-air swirl effect is produced in a cylinder, so that a combustion of the engine is improved. Hence, a fuel economy is improved.